The invention relates to an optical amplifier, and more particularly relates to the use of a single optical amplifier to amplify signals traveling through a plurality of fibers.
A conventional 4-fiber optical amplifier is illustrated in FIG. 1. The optical amplifier node 10 has a first input fiber 12 that couples with a first variable optical attenuator 18 for attenuating optical signals carried over the first input fiber 12. The variable optical attenuator 18 can be either before or after an amplifier 14. In this instance, the optical signals leave the optical attenuator 18 and pass to the amplifier 14. The resulting amplified optical signals exit the amplifier 14 and pass to a first output fiber 16. A second input fiber 20 carries optical signals entering from the same direction for from a second direction opposite the direction of the signals in the first input fiber 12. The second input fiber 20 couples to a second variable optical attenuator 26. The attenuated optical signals pass to a second amplifier 22. The amplified output from the second amplifier 22 passes to the second output fiber 24.
In this conventional optical amplifier node, each signal path requires a separate optical amplifier. As optical amplifiers are costly, the use of multiple amplifiers poses a significant cost for constructing optical networks.
There is a need for an optical amplifier node that uses a single amplifier to amplify signals travelling in different directions, or to use a single amplifier to amplify signals traveling in multiple fibers. The present invention is directed toward further solutions. In accordance with aspects of the present invention, an optical amplifier node has a first and second input fiber in communication with a first combiner. A first amplifier is also in communication with the first combiner. A first de-combiner is in communication with the first amplifier, and first and second output fibers are in communication with the first de-combiner. The first and second input fibers, in accordance with one aspect of the present invention, each support signal traffic traveling in opposite, or the same, directions.
The combiners and de-combiners can take the form of interleavers in accordance with one embodiment of the present invention. The optical interleaver can take an optical signal and separate it into, e.g., odd and even channels when the optical signal passes through the interleaver in a first direction or fiber. A number of odd and even channels can also pass through the interleaver in a second direction, opposite to the first direction, and the interleaver will combine those odd and even signals into a combined signal. Further, a number of odd and even channels can also pass through the interleaver in a second fiber, parallel to the first direction, and the interleaver will combine those odd and even signals into a combined signal. The interleaver can separate and combine other types of signals, and in different ways including by bit, byte, signal, channel, wavelength, band, and the like.
The combiner and de-combiner can also take the form of a number of other network components such as, multiplexors, de-multiplexors, L/C/S combiners and de-combiners, fiber Bragg gratings, thin film filters, holographic filters, and the like.
The optical amplifier node, in accordance with a further aspect of the present invention, has a first variable optical attenuator in communication with one of the first input fiber and the first output fiber. The optical amplifier node further has a second variable optical attenuator in communication with one of the second input fiber and the second output fiber.
In addition, the optical amplifier node can have a second amplifier in communication with an L/C splitter and L/C combiner. The function of the L/C splitter is to separate two wavelength bands spatially into two separate fibers. The C band is commonly defined as 1530 nm to 1565 nm, while the L band is commonly defined as 1570 nm to 1610 nm. The L/C combiner takes two separate C and L wavelength bands, and combines them accordingly. Alternatively, the L/C splitter and combiner can be an L/C/S splitter and an L/C/S combiner. The function of the L/C/S splitter is similar to that of the L/C version, except that the LIC/S splitter separates three wavelength bands spatially into three separate fibers. The S band is commonly defined as 1490 nm to 1525 nm. The L/C/S combiner takes three separate C, L, and S wavelength bands and combines them accordingly.
In addition, the optical amplifier can have a Raman amplifier (co- and/or counter-propagating). The function of the Raman amplifier is to use the nonlinear effect in fibers to impart additional gain to the signals by co- and/or counter-propagating additional Raman pump wavelength signals in the fiber(s). Each fiber must have its own Raman amplifier, unlike the optical amplifier, which can be shared. Alternatively, a single Raman amplifier can be shared between many fibers by using an optical splitter.
Prior to a signal reaching the input of the optical amplifier node, the signal can travel through a multiplexor in communication with the combiner. A dispersion compensation module can be positioned on the communication path between the multiplexor and the first combiner. A dispersion compensation module can also be positioned on the communication path between the first combiner and the first amplifier to compensate for dispersion. Alternatively, the optical amplifier node can have a first amplifier that is a multistage access amplifier with an integrated dispersion compensation module. The dispersion compensation module can be shared between a plurality of fibers.
The optical amplifier node, in accordance with other aspects of the present invention, includes a demultiplexor in communication with the first de-combiner off of the output fiber. A dispersion compensation module can be positioned on the communication path between the demultiplexor and the first de-combiner.
Aspects of the present invention further include a method of amplifying an optical signal. The method begins with routing signal traffic traveling originating from opposite directions, or the same direction, through a first combiner to combine each of the traveling signals into a combined signal. The method continues with routing the combined signal through a first amplifier to amplify that signal. The combined signal is then routed through a first de-combiner to separate the combined signal into the distinct signals traveling in opposite, or the same, directions. The method can further include the step of routing the signals originating from opposite, or the same, directions through variable optical attenuators. Alternatively, the method can include the step of routing the combined signal through an L/C/S splitter, a second amplifier, and an L/C/S combiner.
The signals can travel through one of a multiplexor and a demultiplexor at points external to the amplifier. The method can further include the step of routing the combined signal through a dispersion compensation module, either as a stand-alone module, or as a part of a mid-stage access amplifier having a dispersion compensation module built within.
The optical amplifier node, according to still another aspect of the present invention, can include a first and second input fiber in communication with a first interleaver. The optical amplifier node further includes a first amplifier in communication with the first combiner. A first de-combiner is in communication with the first amplifier. At least two dispersion compensation modules are in communication with the first de-combiner. A second combiner is in communication with at least two dispersion compensation modules. A second amplifier is in communication with the second combiner. A second de-combiner is in communication with the second amplifier, and a first and second output fiber are in communication with the second de-combiner.
In accordance with still another embodiment of the present invention a method of amplifying optical signals is provided beginning with the step of routing a first plurality of signals through a first combiner to form a first combined plurality of signals. A second plurality of signals is routed through a second combiner to form a second combined plurality of signals. The first combined plurality of signals and the second combined plurality of signals are then routed through a third combiner to form a further combined signal. The further combined signal is then routed through an amplifier to generate an amplified signal. The optical signals entering the first, second, and third combiners can be narrow spaced, or wide spaced, channels traveling through single or multiple fibers.